1. Field of the Invention
The present invention relates to a check valve, which is capable of allowing a pressure fluid to flow in one direction along a flow passage while preventing flow of the pressure fluid in an opposite direction.
2. Description of the Related Art
The present applicant has proposed in Japanese Laid-Open Patent Publication No. 2003-322264 (Patent Document 1) a check valve including a body and a pair of couplings disposed on opposite end sides of the body, and which are connected detachably to a pair of fluid pressure devices. The check valve allows the pressure fluid to flow from one of the fluid pressure devices, while preventing flow of the pressure fluid from the other of the fluid pressure devices.
Further, in the check valve disclosed in Japanese Patent No. 3369523 (Patent Document 2), a valve main body is formed from an upstream side body and a downstream side body, wherein the upstream side body and the downstream side body are connected together, and a valve plug and a spring made of a synthetic resin formed in the shape of a compression coil spring are accommodated in the interior of the valve main body. The valve plug is seated on a valve seat under an elastic action of the spring. By supplying a pressure fluid to the interior of the upstream side body, the valve plug is made to separate away from the valve seat in opposition to the elastic force of the spring, and the pressure fluid is allowed to flow to the interior of the downstream side body. On the other hand, in the event that a pressure fluid is supplied to the downstream side body, since the valve plug remains seated on the valve seat and cannot be moved due to the elastic force of the spring, the pressure fluid is prevented from flowing from the downstream side body to the side of the upstream side body.